It is known that, in wireless networks, an Open Service Architecture (OSA) Call Control service capability feature (SCF) provides for application-initiated calls. An application is an entity (usually software) that provides a service to a subscriber. As an example, in an alarm call indication, the user sets the time to be woken up and at the appropriate time, the application calls the user with a predetermined announcement. OSA application-initiated calls are provided by means of a method known as createCall( ) which occurs in the IpCallControlManager interface. In wireless networks supporting Customised Application for Mobile Enhanced Logic CAMEL phase 3 (or lower), the functionality for an application to initiate calls is not provided, as there is no ‘Call Party Handling’ feature as occurs in CAMEL phase 4, in particular no InitiateCallAttempt operation. Although this operation is known to be proposed in Intelligent Networks Capability Set 2 (IN CS-2) for the purpose of network-initiated calls, it will not be implemented in CAMEL networks until CAMEL Phase 4 (Release 5). Instead, in CAMEL phase 3 networks, the mechanism of service properties P_OPERATION_SET described in section 6.5.2 of Third Generation Partnership Project 3GPP technical specification TS 29.198-04 is used to inform the Open Service Architecture OSA client application of this lack of support in a CAMEL service environment CSE, during a service discovery phase.
CCBS (Call Completion to Busy Subscriber) Functionality
A general description of CCBS (call completion to busy subscriber) procedures, referring to FIG. 1, is as follows. As shown in FIG. 1, the CCBS (call completion to busy subscriber) service allows a calling subscriber A (mobile station MS-A), after finding that destination B (mobile station MS-B) is NDUB (Network Determined User Busy), to be notified of when destination B becomes idle (i.e available to receive the call). If subscriber A so desires, the network then automatically generates a CCBS (call completion to busy subscriber) call to destination B. This is often referred to as “ringback” and is as described in Third Generation Partnership Project 3GPP technical specification TS 23.093 CCBS (call completion to busy subscriber) Stage 3. When subscriber A receives a busy treatment (i.e message) from subscriber B, a prolonged call clearing procedure takes place whereby subscriber A invokes a CCBS (call completion to busy subscriber) Activation request. Among other things, this results in the original SETUP message used by subscriber A to setup a call to subscriber B being stored in the home location register (HLR) of subscriber A. As soon as the network detects that subscriber B is available again, the home location register (HLR) of subscriber B (HLR-B) notifies the home location register (HLR) of subscriber A (HLR-A) of this event. Home location register of subscriber A (HLR-A) then sends a mobileapplication part (MAP) Remote User Free (RUF) message (i.e a CCBS (call completion to busy subscriber) remote user free (RUF) message) to the switch (mobile switching centre (MSC)/visitor location register (VLR-A)), currently serving subscriber A. This remote user free (RUF) operation contains the original stored SETUP message. The mobile switching centre (MSC)/visitor location register VLR-A then starts a Network Initiated Mobile Originated (NIMO) process, in which over the radio signalling link, the original SETUP message is sent back to subscriber A (mobile station MS-A) in the CCBS (call completion to busy subscriber) Call Info message. By sending the CCBS (call completion to busy subscriber) Recall message to mobile station MS-A, the network (mobile switching centre (MSC)/visitor location register VLR-A) triggers the mobile station MS-A to initiate the CCBS (call completion to busy subscriber) recall. The original SETUP message is used to setup this CCBS (call completion to busy subscriber) recall to the previously busy subscriber B. Call processing proceeds from here on in a similar way as for normal call processing, i.e. an Initial Address Message (IAM) is sent to the Gateway mobile switching centre GMSC, etc. The home location register HLR-A is notified of the successful setup of the CCBS (call completion to busy subscriber) recall, by means of the CCBS (call completion to busy subscriber) Call Report message from mobile switching centre MSC/visitor location register VLR-A. The reader is referred to the CCBS (call completion to busy subscriber) specifications for a more elaborate background description, namely Third Generation Partnership Project 3GPP technical specifications TS 22.093, TS 23.093, and TS 24.093.